During the supporting period of this investigation different aspects of chromium-cobalt alloys, such as reaction of mold and investment, effect of manipulative variables on physical properties, and behavior of some recently developed alloys for use as dental prosthetic materials, were studied. The effects of addition of previously untried elements are being determined. Through the support of this study, two chromium-cobalt-base alloys were developed with improved physical properties. Both of the newly developed alloys are more ductile (elongation of 10 percent as compared to 2 to 3 percent), both are somewhat softer, and possess the same modulus of elasticity, when compared to other commercially available alloys. The second has about 15 percent higher strength properties than the first alloy. Based on Koster's study, the addition of some elements such as aluminum, boron, titanium, zirconium and niobium should favor formation of fcc phase in cobalt alloys over the hexagonal phase, which in theory should tend to improve ductility. These elements were added to CO-Cr-Ni- $ Ta system and none demonstrated a great improvement in their properties. The ultimate aim of the study is to further improve their mechanical properties and castability. If corrosion resistance of these alloys, along with their mechanics and castability, are improved they may become more suitable for various biomechanical needs.